Current pulse stabilizer for variable loads

ABSTRACT

Amplitude of a fast-rise pulse current is stabilized under varying load conditions by a transformer having a first winding connected in series between a pulse voltage source and a variable load. A square loop hysteresis core of the transformer is biased with regulated DC current in a second winding through a choke coil which stores energy while the bias field is being overcome by a voltage pulse, and restores energy to a power supply for the current pulse source at the end of the current pulse. In a core memory plane, the bias current source services current pulse sources of both polarities for all drive lines and adjacent bit lines are paired with current sources of opposite polarities during read and write cycles to provide tight controlled current loops. Positive and negative energy is returned to the power supply from the choke coil in a substantially balanced manner for both bit (y) and word (x) drive lines.

United States Patent [72] Inventor Wayne R. Brumm 3,233,114 2/1966Eldridge et al 340/174 TB Palos Verdes Peninsula, Calif. 3,263,1257/1966 Genuit 323/9 X [2]] p 25007 Primary Examiner-Gerald Goldberg [22]1970 Attorney-Lindenberg Freidlich & Waserman [45] Patented Nov. 16,1971 [73] Assignee Electronic Memories and Magnetics gig T ABSTRACT:Amplitude of a fast-rise pulse current is stabilngeles,Calil.

lzed under varying load conditions by a. transformer having a m firstwinding connected in series between a pulse voltage [54] CURRENT PULSESTABILIZER FOR VARIABLE source and a variable load. A square loophysteresis core of LOADS the transformer is biased with regulated DCcurrent in a 12 Chhns3Dnwing m second winding through a choke coil whichstores energy while the bias field is being overcome by a voltage pulse,and [52] US. Cl 323/17, restores energy to a power Supply for thecurrent pulse source 323/56 323/66 323/89 340/174 TB at the end of thecurrent pulse. In a core memory plane, the [51] IIILCI G05t3/08 biascurrent Source Services Curran pulse Sources of both [50] Fifild ofSearch 323/6,9, polarities for a drive lines and adjacent bit lines arei d 57,61: 25;:540/17418 with current sources of opposite polaritiesduring read and [56] Reerenccs Cited write cycles to provide tightcontrolled current loops. Positive and negative energy IS returned tothe power supply from the UNITED STATES PATENTS choke coil in asubstantially balanced manner for both bit (y) 2,882,482 4/1959 Simkins340/174 TB and word (I) drive lines.

l4 NEGATIVE POSITIVE V pow: :2 P0 WE R V s u P P L Y s u P P L V l0; I II l l l l l2 (1 '1 LL C0 Lb 5 m PATENTEDauv 1s 19H 3 621 3 71 SHEET 1 or2 NEGATIVE POSITIVE V W R POWER +V SUPPLY SUPPLY lo, 1 I l j I I V I2 tl hill 4 L L Hams 5 I CL 9 H I c; I j f Q 1; 2* 2 WA /AIE R 3211mmQTToQA/EVS CURRENT PULSE STABILIZER FOR VARIABLE LOADS BACKGROUND OF THEINVENTION This invention relates to pulsed current sources for variableloads, and more particularly to pulsed current sources for variableloads that require a substantially constant amplitude for each currentpulse.

In many applications, and particularly in ferrite core memory systems,it is desirable to apply a fast-rise current pulse to a load with asubstantially constant amplitude under varying load conditions. Forexample, in a three wire, 2 iD core memory system, a given N-bit word isread from a group of N cores by selectively applying coincident currentpulses to drive lines which pass through all cores of the group. Theword is read out in parallel by sensing voltage pulses produced on Nseparate sense lines when cores of the group are switched from abinary-l state to a binary-O) state. Since the number of cores in abinary-l state at any one time may vary from to N, the load on the drivecurrent pulse source may vary. Consequently, accurate control of currentamplitude is difiicult to achieve. A substantially constant rise time ofdrive current is also difficult to achieve.

OBJECTS AND SUMMARY OF THE INVENTION An object of this invention is toprovide an improved pulsed current source for use with a variable load.

Another object is to provide an improved control of amplitude for pulsedcurrents applied to core memory systems.

Another object is to provide a common amplitude control system for aplurality of independent pulsed current sources, each source connectedto a different load.

Another object is to provide an amplitude control system for a pluralityof independent pulsed current sources, which system allows setting thecontrol for all pulsed current sources from a single point.

Still another object is to provide an amplitude control system forpulsed current sources in tight controlled current loops to avoidoscillations and minimize noise.

And yet another object is to provide a pulsed current source forvariable loads with fast and substantially constant rise times.

And yet another object is to provide a pulsed current source with anamplitude regulation system for core memory systems with reduced powerrequirements for the total system and reduced power dissipation in theregulation system by restoring both positive and negative energy to thepower supply in a substantially balanced manner.

These and other objects of the invention are achieved by connecting afirst winding of a transformer having a hysteresis loop core and a firstwinding in series with a variable load and a voltage source of a givenpolarity at one end, and a switch for initiating a current pulse throughthe load connected to a voltage source of opposite polarity at the otherend. A second winding of the hysteresis loop transformer is connected inseries with high inductance and a source of regulated DC cur rent tobias the hysteresis loop transformer with a magnetic field of a givenpolarity. The core of the transformer is selected to have a longswitching period in relation to the current pulse period. When theswitch is closed, a current pulse through the first winding produces amagnetic field of opposite polarity to overcome the DC bias field andincrease the applied magnetic field to an upper coercivity level of thehysteresis loop core. Once the core is thus driven to its uppercoercivity level, the hysteresis loop transformer is quickly transformedfrom a low to a high impedance element to limit the amplitude of thecurrent pulse to the load. The inductance in series with the secondwinding stores energy while the core is thus being driven and returns asubstantial part of that energy through a switching diode at the loadend of the transfonner to the system power supply once the current pulseis terminated on the first winding. While energy is thus being returnedby current through the second winding, the core is driven back below itslower coercivity level in order that the hysteresis loop transformer mayonce again function as a stabilizer for a subsequent current pulse: tobe delivered to the load.

In a magnetic core memory, a plurality of hysteresis loop transformersmay be provided, such as one for each bit drive line to selectively readout a word of N bits. The second winding of each hysteresis looptransformer is connected in series with the second winding of all otherhysteresis loop transformers and a source of regulated DC current. Thebias for all hysteresis loop transformersmay then be adjusted from asingle point by adjusting the bias current from the regulated DC currentsource. A second switch is connected in series between the stabilizingtransfonner and the load (core drive line of the magnetic memory). Bothswitches are initially turned on to provide a drive voltage of'2 v.during the current rise time. Then the first switch is turned off duringthe flat top of the current pulse. Once the first switch is turned off,a switching diode connected between circuit ground and a junctionbetween the first switch and the transformer provides a current path toreturn energy to the power supply. By pairing adjacent bit drive linessuch that positive read current is driven in one line in one directionand in the other line in the opposite direction, but from the same endof the array, positive and negative pulse stabilizers may be disposedvery close to each other such that once a switch between the powersupply and the hysteresis loop transformer in each one is opened while aswitch at the other end of each transformer remains closed, a switchingdiode connected to circuit ground is forward biased. That provides adirect current path for return of current from the positive power supplyat the end of one bit line to the negative power supply at the end ofthe other paired bit line, thereby allowing current to be sustained inthe paired bit lines at the maximum level in a tight-controlled loop.

The novel features of the invention, as well as the invention itself,both as to its organization and method of operation, will best beunderstood from the following description in connection with theaccompanying drawings in which like reference characters refer to likeparts.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic diagram of thepresent invention for applying controlled current pulses to a variableload.

FIG. 2 is a graph of applied magnetic field versus flux density in thecore of a hysteresis loop transformer biased for operation in accordancewith the present invention.

FIG. 3 illustrates a plurality of hysteresis loop transformers employedto stabilize current pulses selectively applied to bit drive lines of amagnetic core memory.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, acircuit is shown for obtaining a stabilized amplitude for fast-risecurrent pulses to a variable load It), such as drive line of a magneticcore memory, through a first winding W, of a transformer T having a corewith a hysteresis loop which is substantially square as shown by thecurve in the graph of FIG. 2. That curve passes through points a, b, cand e upon being switched from one saturation state (point a) to asecond saturation state (point e). If the applied magnetic field H isthen decreased, the curve will follow the upper line passing throughpoints 1, g and h back to the point a. The core of the transformer canthus have two remnant states.

In practice, the core of the transformer T, is made of steel in the formof a toroid with a switch time in the order of l microsecond for currentpulses of periods substantially less than 1 microsecond, such as /4 of amicrosecond. That will assure that the core will not be driven from theone saturation state at point a to the second saturation state at pointe during a current pulse period. Instead, the core is driven throughonly points a, b, c and d. Between points a and b, the impedance of thetransformer winding W, is low to allow a rapid rise of the current pulsethrough the load to a predetermined maximum amplitude determined by thebias which separates points a and 12. Once the applied magnetic fieldreaches the coercivity of the core represented by the line betweenpoints b and c, the transformer winding W, presents a high impedance tolimit the current thereby producing a current pulse with a fast risetime and a flat top. Before the core reaches point e, and preferablywhile it is being driven through a linear portion near the point 0,transistors Q, and Q, are turned off to remove current drive through theload. The result is a current pulse with a fast fall time from the flattop as the core is returned to point a along the dotted line from pointd to g.

When the load 10 is a magnetic core drive line, turning off thetransistor Q, may produce resonance in the line. Accordingly, althoughnot shown, it is understood that proper measures are taken to.achievenecessary damping and termination of the drive line. Standard techniqueshave been developed for damping and tennination of magnetic core drivelines which, for a first approximation, may be thought of as N paralleltransmission lines.

A source 1 l of regulated DC current is applied to a second winding ofthe transformer T, through a choke coil 12 which presents sufficientlyhigh inductance to stabilize bias current to the second winding W, ofthe transformer.

The regulated DC current from the source 1] establishes a DC bias fieldrepresented in FIG. 2 by a dotted line H This DC bias field is stableunder static conditions due to the regulation of current from the source11, and under dynamic conditions due to the inductance of the choke coil12.

The transistor 0, is connected as a series switch in a form conventionalin a core memory system, namely a floating transformer coupledtransistor switch employed as a voltage switch by having its emitterconnected to a negative terminal (-V) of a DC power supply and atransformer T, having its secondary winding connected across thebase-emitter junction of the transistor 0,. The transistor Q, issimilarly connected as a series switch with its collector connected tothe positive terminal of aDC power supply 14 and a transformer acrossits base-emitter junction. When timing pulses are applied across theprimary windings of the transfonners T and T the baseemitter junctionsof the transistors Q, and Q, are forward biased, thereby causing currentto flow from a positive terminal (-l-V) of the power supply 14 throughthe load 10 and the first winding W, of the transformer T, to thenegative terminal of the (-V) of the power supply 13.

Turning on both transistors Q, and Q, simultaneously will establish adrive voltage of 2 v. during the rise time of the current pulse throughthe load 10 for a more rapid rise of the current pulse. Once sufl'lcienttime has been allowed for the core to be driven to the linear portion ofits hysteresis loop between points b and c, the transistor Q, is turnedoff. A switching diode D, then becomes forward biased to provide areturn path for sustaining current through the load during the flat topperiod of the current pulse. In that manner, current quickly rises to amaximum level in response to a drive voltage of 2 v. and is thensustained with a drive voltage of only lv. When the transistor 0, islater turned off, at a time before the core of the transformer T, isswitched to the second saturation point e, a switching diode D will alsobecome forward biased to return negative energy to the power supply 13,as will be presently described more fully. In that manner, thehysteresis loop of the core in the transformer T, stabilizes theamplitude of the resulting current pulse to a predetermined level undervarious load conditions of the load 10.

As noted hereinbefore, FIG. 2 indicates the effect of the square loopcharacteristics of the transfonner 12 in stabilizing the current pulse.Once the transistor 0, is turned on, current will increase very quicklyuntil the bias field is overcome and further increase in currentincreases the magnetic field beyond the point 11. In that manner, theimpedance of the transformer winding W, changes from a low to a highvalue, and the current through the load is efiectively stabilized whilethe magnetic field drives the core from point b toward point d toprovide a precise, fast-rise current pulse which is independent of thecondition of the load 10. This independence is due to the high impedanceof the transformer T, once its core has been driven past point b, andthe stabilizing effect of the transformer T, on the current while itscore is being driven toward point d. If a sufficiently slow core isused, point d may be before point 0, but the cost of such cores issignificantly greater.

While the core of the transformer T, is being driven from point a towardpoint d and then back to point a, some energy is dissipated in the core,and some stored in the magnetic field of the choke coil 12 is returnedto the power supply 13. Thus, when the transistor Q, is turned off, thepolarity and density of the core flux will then change over the pathd-g-h-a. As is well known, the energy within the hysteresis looprepresents energy dissipated as heat in the transfonner T,. Therefore,the material for the core should ideally be selected to have as thin aloop as possible, and yet be sufiiciently slow to avoid driving it toits second saturation point before the current pulse is terminated.

The energy stored in the inductor 12, not dissipated in the core, isreturned to the negative power supply 13 through a path which includesdiodes D, and D Thus, as the collapsing field of the choke coil 12drives the core of the transfonner T, back to point a, the voltage pulseinduced in the first winding W, forward biases the diodes D, and D, toreturn energy to the power supply 13.

The second winding W of the transformer T, may be connected in serieswith the corresponding second winding of other hysteresis looptransformers employed to stabilize current pulses from independentsources through separate loads. Such an arrangement is illustrated inFIG. 3 which shows (by way of example, and not by way of limitation) aportion of a three wire, 2 %D coincident current core memory having aplurality N of bit lines for a matrix of MN cores arranged in M groupsof N cores such that the bit cores of any one group may be switched tothe zero state to read out a given N-bit word in response to a currentpulse in a given orthogonal word line (not shown) and a positive currentis driven through the bit line L, in a direction indicated by an arrow+I when transistors are actuated in the manner described with referenceto FIG. 1. When the word line through the core is driven with current inthe same direction, the core is switched. The word line pulse is delayeduntil the bit line pulse has reached its flat top in order that thebinary digit read may be sensed on the bit line L (by means not shown)as a pulse if the digit is a binary-1.

A second bit line L, of the matrix is shown to better illustrate how thepresent invention may be used to restorenegative and positive energy tothe power supplies l3 and 14 (FIG. 1) in a balanced manner during amemory cycle. Transistors Q and Q, are connected as floating transformerswitches to selection diodes D, and D, through the line L, for read andwrite memory cycles. Thus, to read line L,, the transistor 0;, is turnedon while transistors Q, and Q, are on. This provides an initial drivevoltage of 2 v. through the diode D Then the transistor Q, is turned011' to provide a pulse sustaining voltage of l v. the transistor Q, isturned off with the transistor Q, to complete a read cycle. Negativeenergy stored by the inductor l2, and other inductance associated withthe bias circuit, is then returned to the power supply 13 via the diodeD,.

A read cycle is usually followed immediately by a write cycle in amemory access cycle. To drive negative current through the line L,,transistors Q, to Q, are actuated in the same manner as transistors Q,to 0 using a separate transformer T, to stabilize the resulting negativecurrent pulse. After all transistors Q, to Q have been turned off toterminate the negative current pulse, the winding of the transformer T,in series with the bias stabilizing inductor 12 will induce a voltageacross the winding connected to switching diodes D and D, to forwardbias the diode D,,. In that manner, positive energy is restored throughthe diode D to the power supply 14 (FIG. I).

Transistors O and Q are similarly actuated with transistor Q,, for aselective positive read current pulse through a trans former T and theline L Transistors Q,,, to 0,, are actuated like transistors Q, to for aselective negative write current pulse through a transformer T, and aline L Other lines are selectively driven using cycle controltransistors like transistors 0 and Q, and separate positive and negativecurrent pulse stabilizing arrangement for each line.

As a result of driving adjacent bit lines in opposite directions for aread or a write cycle, and juxtaposing the pulse stabilizingtransformers of conjugate lines for read and write cycles as shown,tight controlled loops are provided for read and write pulse currents inconjugate lines through switching diodes connected to circuit ground.For example, transistors Q, and connect transformers T, and T tonegative and positive power supplies for a read cycle to drive positivecurrents through the drive lines L, and L When those transistors areturned off after the initial pulse rise time, diodes D, and D becomeforward biased to provide return current paths to circuit groundformerly provided by the transistors through power supplies of oppositepolarities. Since the impedances of the forward biased diodes D, and Dto AC signals are very low, as compared to impedances of current pathsthrough the circuit ground from the diodes D, and D to the powersupplies, AC or pulse current from the positive power supply is driventhrough the line L, and returned to the negative power supply throughthe line L via diodes D, and D, rather than though circuit ground.

All of the bias windings of the stabilizing transformers are connectedin series with the inductor l2 and the constant current source 11.However, in practice not more than approximately six transformers shouldbe so connected in a group without some series inductance between groupsto store energy. in other words, the storage inductance for the seriesconnected transformers should be distributed between groups of not morethan about six.

The arrangement of FIG. 3 may be used for word drive lines in a similarmanner. However, since only one line is driven at any given time, thereturn path for the current pulse is through circuit ground, and notthrough another line as in the case of conjugate bit drive lines.However, other advantages, including the balanced return of energy tothe power supplies, are retained.

In the cores of bit drive lines, the balanced return results from theoperation of oppositely poled read pulse stabilizers associated withconjugate lines for all lines during a read cycle. During a write cycle,current will be driven through only those lines storing a bit 1.Therefore, the balance is not complete during any given write cycle, butis complete over a large number of cycles. For instance, if a bit 0 isto be stored in line L, while a bit 1 is stored in line L only thetransistor 0, is turned, and not the transistor 0,. The return path fornegative current through the line L is through a diode D, and circuitground once the transistor 010 is turned off. When the transistor 0,, isturned off, energy is restored in the positive power supply throughdiode D Energy is not simultaneously restored in the negative powersupply. However, during another write cycle a bit 1 may be stored in theline L, and not in the line L, so that energy is then restored only inthe negative power supply. Thus, over a large number of write cycles,the balance will be substantially complete.

in the case of word drive lines, each read cycle is normally followed bya write cycle. When oppositely poled pulse stabilizers are thus used forread and write cycles, the positive ener gy restored in one cyclebalances the negative energy restored in the other cycle.

Since the present invention does not employ feedback for stabilization,there is no possibility of oscillation. Another advantage is that sincea common regulated DC current source 11 is employed for all currentpulse stabilizing transformers,

control of all current pulse sources is achieved from a single point.That allows variation of the amplitude of all current pulse sources witha common control on the regulated DC source 11, i.e., with a commoncontrol of the bias field for all hysteresis loop transformers.

Although a particular embodiment of the invention has been described andillustrated herein, it is recognized that modifications and variationswill be obvious to those skilled in the art. For example, by usingindependent pulse stabilizers substantially as shown in FIG. 1 for bitdrive lines as well as word drive lines, the present invention may beemployed in a two wire, 2%D memory system. Other modifications mayinclude additional levels of selection switches, and other switchingarrangements including the arrangement for the switching diodes. Forexample, for the read drive current through the line L,, energy can bereturned to the positive power supply by connecting the diode D tocircuit ground and the diode D, to the positive power supply. If that isdone, the switch 0-, could be omitted if a drive voltage of 2 v. is tobe retained throughout the entire pulse period. However, the embodimentillustrated is preferred even though two switches are required becausethat allows the initial drive voltage of 2 v. to be larger for a fasterrise of the pulse without overstressing switching components since thedrive voltage is then quickly cut back to l v. Accordingly, since somany modifications and variations are possible, it is intended that theclaims be interpreted to cover all modifications and variations thatwill be obvious to those skilled in the art and equivalents thereof.

What is claimed is:

1. Apparatus for stabilizing a pulse of current fonn a source of DCpower through a variable load comprising:

a transformer with a square-loop hysteresis core having a predeterminedcoercivity level of current required for switching it from saturation ata given polarity, said transformer having first and second windings;

means including inductance in series with said second winding fordriving regulated DC bias current through said second winding tosaturate said core at said given polariy;

switching means for coupling said source of DC power in a series circuitwith said load and said first winding to drive current through said loadin a given direction, the polarity of said first winding relative tosaid second winding being such that current through said first windingwill drive said core from saturation at said given polarity towardsaturation at said opposite polarity, said switching means being activeto drive said current through said load for a period of time sufficientto reach said coercivity level of current and less than necessary todrive said core to saturation at said opposite polarity; and

a pair of diodes connected to opposite ends of said first winding, oneof said diodes being connected to said power supply and poled forforward conduction in,

response to induced current in said first winding when current throughsaid load is terminated by said switching means, and the other of saiddiode being connected and poled to provide a return circuit for inducedcurrent in said first winding, whereby energy stored in said bias meansis returned to said source of power.

2. Apparatus as defined in claim 1 wherein one end of said load remotefrom said first winding; is coupled to circuit ground, said switchingmeans comprises a series switch coupling said source of power to saidfirst winding at an end thereof remote from said load said source ofpower is connected between said series switch and circuit ground, saidone of said diodes is connected between circuit ground and said firstwinding at an end thereof remote from said load, and the other of saiddiodes is connected between said power source and said first winding atan end thereof remote from said power source.

3. A current pulse stabilizer for a variable load comprising:

means DC coupling one end of said load to circuit ground;

a first transformer with a squareloop hysteresis core having first andsecond windings;

a choke coil connected in series with said second winding;

a source of regulated DC bias current connected in series with saidchoke coil and said second winding for driving current through saidsecond winding in a direction for biasing said core beyond a saturationpoint of a given polarity;

a source of DC power having one terminal at a given polarity and anotherterminal connected to circuit ground;

switching means for DC coupling said one terminal of said power supplyto said load through said first winding to drive current in a givendirection through said load to circuit ground, the polarity of saidfirst winding relative to said second winding being such that currentthrough said first winding will cancel fiux in said core produced bybias current in said second winding, said switching means being activeto produce said current pulse for a period of time less than necessaryto drive said core through said saturation point of said given polarityto a saturation point of opposite polarity; and

a pair of diodes connected to opposite ends of said first winding, oneof said diodes being connected between circuit ground and one terminalof said first winding adjacent said source of power, and the other ofsaid diodes being connected between said one terminal of said source ofpower and the other terminal of said first winding adjacent said load,said pair of diodes being poled for forward conduction in response toinduced current from said second winding when current through said loadis terminated by said switching means, whereby energy stored in saidcoil while current is driven through said load is returned to saidsource of power.

4. A current pulse stabilizer as defined in claim 3 wherein said meansDC coupling one end of said load to circuit ground includes a source ofpower having one terminal connected to circuit ground and a secondtenninal at a polarity opposite said given polarity, and said switchingmeans comprises two series switches, one at each end of said firstwinding, whereby one switch remote from said load may be activated withthe other switch during the current pulse rise time to provide a drivevoltage equal to the sum of potentials of said sources of power atopposite ends of said load, and then deactivated to provide a drivevoltage for sustaining current through said load equal to the potentialof said source of power at said one end of said load.

5. A current pulse stabilizer as defined in claim 4 wherein said load isa core drive line of a magnetic core through which current must bedriven in either direction, further including:

a second transformer with a square-loop hysteresis core having first andsecond windings, said second winding being connected in series with saidchoke coil to receive said bias current;

a separately controlled switch at each end of said first winding of saidsecond transfonner coupling said first winding in series with said loadat the end thereof opposite said one end, and in series with said sourceof powerof opposite polarity for operation in substantially the samemanner as corresponding switches connected to said first winding of saidfirst transformer, the polarity of said first winding of said secondtransformer being such that current therethrough will cancel flux insaid core of said second transformer produced by bias current in saidsecond winding of said second transformer for current through said loadin a direction opposite said given direction;

a second pair of diodes, one of said second pair of diodes connectedbetween circuit ground and said first winding of said second transformerat the end thereof remote from said load, and the other of said secondpair of diodes connected between said source of power of oppositepolarity and said first winding of said second transformer at the endthereof next to said load, said second pair of diodes being poled forforward conduction in response to induced current from said secondwinding of said second transformer when current through said load andsaid first winding of said second transformer is terminated, wherebyenergy stored in said coil, while current is driven through said load ina direction opposite said given direction, is returned to said powersupply of opposite polarity;

a second source of power having one tenninal of a polarity opposite saidgiven polarity and another tenninal connected to circuit ground; and

means for selectively coupling said load at the end thereof remote fromsaid first and second transformers to one power source terminal of saidgiven polarity when said switches connected to said first transformerare activated and, to said one power source terminal of oppositepolarity when said switches connected to said second transformer areactivated.

6. In combination: 1

a load through which a fast-rise current pulse is to be driven with astable amplitude for different values of load impedance, said load beingDC coupled at one end to circuit ground;

means DC coupling one end of said load to circuit ground;

a first transformer with a square-loop hysteresis core having first andsecond windings;

means including a choke coil for driving regulated DC bias currentthrough said second winding in a direction for biasing said core beyonda saturation point of a given polarity;

a source of DC power having one terminal at a given polarity and anotherterminal connected to circuit ground;

first switching means at one end of said first winding for DC couplingsaid first winding in series with said load;

second switching means connected to said one terminal of said source ofpower for DC coupling said source of power to said first winding todrive current in a given direction through said load to circuit ground,the polarity of said first winding relative to said second winding beingsuch that current through said first winding will cancel flux in saidcore produced by bias current in said second winding, said first andsecond switching means being active for a period of time less thannecessary to drive said core through said saturation point of said givenpolarity to a saturation point of opposite polarity; and

a first diode connected between circuit ground and said one end of saidfirst winding, and a second diode connected between said one terminal ofsaid source of power and said first winding at an end thereof oppositesaid one end, said first and second diodes being poled for forwardconduction in response to induced current from said second winding whencurrent through said load is terminated by said first and secondswitching means, whereby energy stored in said coil while current isdriven through said load is returned to said source of power.

7. A combination as defined in claim 6 wherein said means coupling saidone end of said load to said circuit ground includes a second source ofpower having one terminal of polarity opposite said given polarity DCcoupled to said load and another terminal connected to circuit ground,and wherein said first and second switching means are separatelycontrolled, whereby both switching means may be activated initially toprovide a drive voltage for current through said load equal to the sumof output voltages from said sources of power coupled to opposite endsof said load, and said first switching means at said one end of saidfirst transformer winding may be deactivated at the end of the rise timeof current through said load to reduce the drive voltage to that coupledto the end of said first transformer winding through said load until theend of the current pulse, at which time said second switching means maybe deactivated.

8. A combination as defined in claim 7 wherein said load is a core driveline of a magnetic core through which current must be driven in eitherdirection, further including:

a second transformer with a square-loop hysteresis core having a firstwinding and a second winding, said second winding being connected inseries with said choke coil and said second winding of said firsttransformer to receive bias current;

separately controlled switching means at each end of said first windingof said second transformer coupling said first winding in series withsaid load at the end thereof opposite said one end, and in series withsaid source of power of opposite polarity for operation in substantiallythe same manner as corresponding switching means connected to said firstwinding of said first transformer, the polarity of said first winding ofsaid first transformer being such that current therethrough will cancelflux in said core of said second transformer produced by bias current insaid second winding of said second transformer for current through saidload in a direction opposite said given direction;

a third diode connected between circuit ground and said first winding ofsaid second transformer at the end thereof remote from said load, and afourth diode connected between said source of power of opposite polarityand said first winding of said second transformer at the end thereofnext to said load, said third and fourth diodes being poled for forwardconduction in response to induced current from said second winding ofsaid second transformer when current through said load and said firstwinding of said second transformer is terminated, whereby energy storedin said coil, while current is driven through said load in a directionopposite said given direction, is returned to said power supply ofopposite polarity; and

a means for coupling said load at the end thereof remote from said firstand second transformers to said one terminal of said source of power ofsaid given polarity when said separately controlled switching meansconnected to said second transformer are activated, and to said oneterminal of said second source of power when said first and secondswitching means connected to said first transformer are actuated.

9. ln a bipolar current drive system for bit drive lines of a magneticcore memory wherein said drive lines are divided into two groups withcurrent in lines are divided into two groups with current in lines ofone group opposite current in lines of the other group, and wherein agiven line in one group is paired with a given line in the other, a pairof current pulse stabilizers comprising:

first and second transformers, each with a square-loop hysteresis corehaving a predetermined coercivity level of current required forswitching it from saturation at a given polarity to saturation at anopposite polarity;

bias means including inductance in series with said second winding fordriving regulated DC bias current through the second winding of eachtransformer in series to saturate each transformer at said givenpolarity;

negative and positive sources of DC power, said negative source havingone terminal connected to circuit ground said positive source having oneterminal connected to circuit ground, whereby negative and positivecurrent drive potentials are provided with respect to circuit ground;

first and second switching means for coupling said first and secondsources of power in series circuits with respective ones of said pairedlines and said first winding of said first and second transformers,respectively, to drive current through said paired lines in oppositedirections, the polarity of said first winding relative to said secondwinding in each of said first and second transformers being such thatcurrent through said first winding will drive said core from saturationat said given polarity toward saturation at said opposite polarity, saidfirst and second switching means being active to drive said currentsthrough said given lines for a period of time sufficient to reach saidcoercivity level of current and less than necessary to drive said coreto saturation at said opposite polarity; and

two pairs of diodes, one pair for each transformer, one

diode of a given pair being connected between said first winding of agiven transformer at the end remote from the source of power to whichsaid first winding is connected, and the other diode of said given pairbeing connected between said first winding of said given transformer atthe end adjacent to said source of power to which said first winding isconnected and circuit ground, each pair of diodes being poled forforward conduction in response to induced current in said first windingto which connected when said first and second switching means terminatecurrents through said lines, whereby energy stored in said bias means isreturned to said sources of power in a substantially balanced mannerfrom said inductance in said bias means.

10. The combination as defined in claim 9 wherein one end of each lineof said pair remote from said transformers is coupled to circuit groundby respective first and second switching means and said positive andnegative sources of power, and a given one of said first and secondswitching means comprises a first series switch at one end of said firstwinding of a transformer coupled to a source of power and a secondseries switch at the other end of said first winding of a transformercoupled to a line, whereby said first and second switches of a givenswitching means may be activated simultaneously to initiate current witha drive voltage equal to twice the potential of a given power source,and said first switch may be deactivated before said second switch tomaintain drive current with a drive voltage equal to the potential of agiven power source, said drive current being maintained through one ofsaid paired diodes connected to circuit ground, whereby atight-controlled pulsed current loop is maintained from one to the otherof said paired lines through said diodes connected to circuit ground.

11. The combination as defined in claim 10 further comprising a secondpair of current pulse stabilizers for said paired lines identical tosaid first pair but oppositely connected to said paired lines such thatsimultaneous currents in opposite directions are reversed fromdirections of currents produced by said first pair of currentstabilizers when said second pair of current stabilizers are activatedby first and second switching means of said second pair.

12. The combination as defined in claim 11 wherein all second windingsof all transformers are connected in a singleseries circuit of said biasmeans.

1. Apparatus for stabilizing a pulse of current form a source of DCpower through a variable load comprising: a transformer with asquare-loop hysteresis core having a predetermined coercivity level ofcurrent required for switching it from saturation at a given polarity,said transformer having first and second windings; means includinginductance in series with said second winding for driving regulated DCbias current through said second winding to saturate said core at saidgiven polarity; switching means for coupling said source of DC power ina series circuit with said load and said first winding to drive currentthrough said load in a given direction, the polarity of said firstwinding relative to said second winding being such that current throughsaid first winding will drive said core from saturation at said givenpolarity toward saturation at said opposite polarity, said switchingmeans being active to drive said current through said load for a periodof time sufficient to reach said coercivity level of current and lessthan necessary to drive said core to saturation at said oppositepolarity; and a pair of diodes connected to opposite ends of said firstwinding, one of said diodes being connected to said power supply andpoled for forward conduction in response to induced current in saidfirst winding when current through said load is terminated by saidswitching means, and the other of said diode being connected and poledto provide a return circuit for induced current in said first winding,whereby energy stored in said bias means is returned to said source ofpower.
 2. Apparatus as defined in claim 1 wherein one end of said loadremote from said first winding is coupled to circuit ground, saidswitching means comprises a series switch coupling said source of powerto said first winding at an end thereof remote from said load saidsource of power is connected between said series switch and circuitground, said one of said diodes is connected between circuit ground andsaid first winding at an end thereof remote from said load, and theother of said diodes is connected between said power source and saidfirst winding at an end thereof remote from said power source.
 3. Acurrent pulse stabilizer for a variable load comprising: means DCcoupling one end of said load to circuit ground; a first transformerwith a square-loop hysteresis core having first and second windings; achoke coil connected in series with said second winding; a source ofregulated DC bias current connected in series with said choke coil andsaid second winding for driving current through said second winding in adirection for biasing said core beyond a saturation point of a givenpolarity; a source of DC power having one terminal at a given polarityand another terminal connected to circuit ground; switching means for DCcoupling said one terminal of said power supply to said load throughsaid first winding to drive current in a given direction through saidload to circuit ground, the polarity of said first winding relative tosaid second winding being such that current through said first windingwill cancel flux in said core produced by bias current in said secondwinding, said switching means being active to produce said current pulsefor a period of time less than necessary to drive said core through saidsaturation point of said given polarity to a saturation point ofopposite polarity; and a pair of diodes connected to opposite ends ofsaid first winding, one of said diodes being connected between circuitground and one terminal of said first winding adjacent said source ofpower, and the other of said diodes being connected between said oneterminal of said source of power and the other terminal of said firstwinding adjacent said load, said pair of diodes being poled for forwardconduction in response to induced current from said second winding whencurrent through said load is terminated by said switching means, wherebyenergy stored in said coil while current is driven through said load isreturned to said source of power.
 4. A current pulse stabilizer asdefined in claim 3 wherein said means DC coupling one end of said loadto circuit ground includes a source of power having one terminalconnected to circuit ground and a second terminal at a polarity oppositesaid given polarity, and said switching means comprises two seriesswitches, one at each end of said first winding, whereby one switchremote from said load may be activated with the other switch during thecurrent pulse rise time to provide a drive voltage equal to the sum ofpotentials of said sources of power at opposite ends of said load, andthen deactivated to provide a drive voltage for sustaining currentthrough said load equal to the potential of said source of power at saidone end of said load.
 5. A current pulse stabilizer as defined in claim4 wherein said load is a core drive line of a magnetic core throughwhich current must be driven in either direction, further including: asecond transformer with a square-loop hysteresis core having first andsecond windings, said second winding being connected in series with saidchoke coil to receive said bias current; a separately controlled switchat each end of said first winding of said second transformer couplingsaid first winding in series with said load at the end thereof oppositesaid one end, and in series with said source of power of oppositepolarity for operation in substantially the same manner as correspondingswitches connected to said first winding of said first transformer, thepolarity of said first winding of said second transformer being suchthat current therethrough will cancel flux in said core of said secondtransformer produced by bias current in said second winding of saidsecond transformer for current through said load in a direction oppositesaid given direction; a second pair of diodes, one of said second pairof diodes connected between circuit ground and said first winding ofsaid second transformer at the end thereof remote from said load, andthe other of said second pair of diodes connected between said source ofpower of opposite polarity and said first winding of said secondtransformer at the end thereof next to said load, said second pair ofdiodes being poled for forward conduction in response to induced currentfrom said second winding of said second transformer when current throughsaid load and said first winding of said second transformer isterminated, whereby energy stored in said coil, while current is driventhrough said load in a direction opposite said given direction, isreturned to said power supply of opposite polarity; a second source ofpower having one terminal of a polarity opposite said given polarity andanother terminal connected to circuit ground; and means for selectivelycoupling said load at the end thereof remote from said first and secondtransformers to one power source terminal of said given polarity whensaid switches connected to said first transformer are activated and, tosaid one power source terminal of opposite polarity when said switchesconnected to said second transformer are activated.
 6. In combination: aload through which a fast-rise current pulse is to be driven with astable amplitude for different values of load impedance, said load beingDC coupled at one end to circuit ground; means DC coupling one end ofsaid load to circuit ground; a first transformer with a square-loophysteresis core having first and second windings; means including achoke coil for driving regulated DC bias current through said secondwinding in a direction for biasing said core beyond a saturation pointof a given polarity; a source of DC power having one terminal at a givenpolarity and another terminal connected to circuit ground; firstswitching means at one end of said first winding for DC coupling saidfirst winding in series with said load; second switching means connectedto said one terminal of said source of power for DC coupling said sourceof power to said first winding to drive current in a given directionthrough said load to circuit ground, the polarity of said first windingrelative to said second winding being such that current through saidfirst winding will cancel flux in said core produced by bias current insaid second winding, said first and second switching means being activefor a period of time less than necessary to drive said core through saidsaturation point of said given polarity to a saturation point ofopposite polarity; and a first diode connected between circuit groundand said one end of said first winding, and a second diode connectedbetween said one terminal of said source of power and said first windingat an end thereof opposite said one end, said first and second diodesbeing poled for forward conduction in response to induced current fromsaid second winding when current through said load is terminated by saidfirst and second switching means, whereby energy stored in said coilwhile current is driven through said load is returned to said source ofpower.
 7. A combination as defined in claim 6 wherein said meanscoupling said one end of said load to said circuit ground includes asecond source of power having one terminal of a polarity opposite saidgiven polarity DC coupled to said load and another terminal connected tocircuit ground, and wherein said first and second switching means areseparately controlled, whereby both switching means may be activatedinitially to provide a drive voltage for current through said load equalto the sum of output voltages from said sources of power coupled toopposite ends of said load, and said first switching means at said oneend of said first transformer winding may be deactivated at the end ofthe rise time of current through said load to reduce the drive voltageto that coupled to the end of said first transformer winding throughsaid load until the end of the current pulse, at which time said secondswitching means may be deactivated.
 8. A combination as defined in claim7 wherein said load is a core drive line of a magnetic core throughwhich current must be driven in either direction, further including: asecond transformer with a square-loop hysteresis core having a firstwinding and a second winding, said second winding being connected inseries with said choke coil and said second winding of said firsttransfoRmer to receive bias current; separately controlled switchingmeans at each end of said first winding of said second transformercoupling said first winding in series with said load at the end thereofopposite said one end, and in series with said source of power ofopposite polarity for operation in substantially the same manner ascorresponding switching means connected to said first winding of saidfirst transformer, the polarity of said first winding of said firsttransformer being such that current therethrough will cancel flux insaid core of said second transformer produced by bias current in saidsecond winding of said second transformer for current through said loadin a direction opposite said given direction; a third diode connectedbetween circuit ground and said first winding of said second transformerat the end thereof remote from said load, and a fourth diode connectedbetween said source of power of opposite polarity and said first windingof said second transformer at the end thereof next to said load, saidthird and fourth diodes being poled for forward conduction in responseto induced current from said second winding of said second transformerwhen current through said load and said first winding of said secondtransformer is terminated, whereby energy stored in said coil, whilecurrent is driven through said load in a direction opposite said givendirection, is returned to said power supply of opposite polarity; and ameans for coupling said load at the end thereof remote from said firstand second transformers to said one terminal of said source of power ofsaid given polarity when said separately controlled switching meansconnected to said second transformer are activated, and to said oneterminal of said second source of power when said first and secondswitching means connected to said first transformer are actuated.
 9. Ina bipolar current drive system for bit drive lines of a magnetic corememory wherein said drive lines are divided into two groups with currentin lines of one group opposite current in lines of the other group, andwherein a given line in one group is paired with a given line in theother, a pair of current pulse stabilizers comprising: first and secondtransformers, each with a square-loop hysteresis core having apredetermined coercivity level of current required for switching it fromsaturation at a given polarity to saturation at an opposite polarity;bias means including inductance in series with said second winding fordriving regulated DC bias current through the second winding of eachtransformer in series to saturate each transformer at said givenpolarity; negative and positive sources of DC power, said negativesource having one terminal connected to circuit ground said positivesource having one terminal connected to circuit ground, whereby negativeand positive current drive potentials are provided with respect tocircuit ground; first and second switching means for coupling said firstand second sources of power in series circuits with respective ones ofsaid paired lines and said first winding of said first and secondtransformers, respectively, to drive current through said paired linesin opposite directions, the polarity of said first winding relative tosaid second winding in each of said first and second transformers beingsuch that current through said first winding will drive said core fromsaturation at said given polarity toward saturation at said oppositepolarity, said first and second switching means being active to drivesaid currents through said given lines for a period of time sufficientto reach said coercivity level of current and less than necessary todrive said core to saturation at said opposite polarity; and two pairsof diodes, one pair for each transformer, one diode of a given pairbeing connected between said first winding of a given transformer at theend remote from the source of power to which said first winding isconnected, and the other diode of said given pair being connectedbetween said first winding of said given transformer at the end adjacentto said source of power to which said first winding is connected andcircuit ground, each pair of diodes being poled for forward conductionin response to induced current in said first winding to which connectedwhen said first and second switching means terminate currents throughsaid lines, whereby energy stored in said bias means is returned to saidsources of power in a substantially balanced manner from said inductancein said bias means.
 10. The combination as defined in claim 9 whereinone end of each line of said pair remote from said transformers iscoupled to circuit ground by respective first and second switching meansand said positive and negative sources of power, and a given one of saidfirst and second switching means comprises a first series switch at oneend of said first winding of a transformer coupled to a source of powerand a second series switch at the other end of said first winding of atransformer coupled to a line, whereby said first and second switches ofa given switching means may be activated simultaneously to initiatecurrent with a drive voltage equal to twice the potential of a givenpower source, and said first switch may be deactivated before saidsecond switch to maintain drive current with a drive voltage equal tothe potential of a given power source, said drive current beingmaintained through one of said paired diodes connected to circuitground, whereby a tight-controlled pulsed current loop is maintainedfrom one to the other of said paired lines through said diodes connectedto circuit ground.
 11. The combination as defined in claim 10 furthercomprising a second pair of current pulse stabilizers for said pairedlines identical to said first pair but oppositely connected to saidpaired lines such that simultaneous currents in opposite directions arereversed from directions of currents produced by said first pair ofcurrent stabilizers when said second pair of current stabilizers areactivated by first and second switching means of said second pair. 12.The combination as defined in claim 11 wherein all second windings ofall transformers are connected in a single-series circuit of said biasmeans.